Impact of plant flowering phenology on the cost/benefit balance in a nursery pollination mutualism,with honest males and cheating females

This study documents the flowering phenology and its potential consequences on a nursery pollination mutualism between a dioecious plant, in which honest male plants, but not cheating females, allow the specific pollinator to reproduce within inflorescences. Very few pollinators were found to emerge during plant anthesis, leading to a low (if any) potential benefit through pollen dispersal. This opens the question why male plants do not also cheat their pollinators. Female plants flowered late in the season, when many males had just achieved their own anthesis, which increased the efficiency of pollen transfer. Finally, some late‐flowering males reached their anthesis simultaneously with females, which open the possibility for pollinator to choose between honest males and cheating females. Nevertheless, female plants were found to produce fruits, even though fruit production was limited by pollen (and pollinator) supply, meaning that cheating was not entirely retaliated by the mutualistic partner.     

'Inconstant males' and the maintenance of labile sex expression in subdioecious plants

* Here, we evaluate the role of pollen limitation and selfing in the maintenance of labile sex expression in subdioecious plant species. * We used a literature survey to explore which factors correlated with a significant occurrence of hermaphrodites in dioecious species. We developed models to explore the selective maintenance of labile sex expression. The models had similar ecological assumptions but differed in the genetic basis of sex lability. * We found that a significant frequency of hermaphrodites was associated with animal pollination, and that hermaphrodites were 'inconstant' males with perfect flowers, suggesting evolution through the gynodioecious pathway. Models showed that a modifier converting pure males into inconstant males could be maintained under a wide range of reduction in both male and female fitness. Pollen limitation and self-fertilization facilitated invasion of the modifier. Depending on the genetics of sex determination, we found pure dioecy, stable subdioecy (trioecy), and situations where inconstant males coexisted with either pure females or pure males. Under selfing and pollen limitation, certain conditions selected for inconstant males which will drive populations to extinction. * We discuss our results in relation to the evolution towards, and the breakdown of, dioecy, and the ecological and evolutionary implications of labile sex expression.     

Pollen limitation,fruit abortion,and autonomous selfing in three populations of the perennial herb Ruellia nudiflora

Multiple factors determine plant reproductive success and their influence may vary spatially. This study addresses several factors influencing female reproductive success in three populations of Ruellia nudiflora, specifically we: (i) determine if fruit set is pollen‐limited and if pollinator visitation rates are related to this condition; (ii) estimate fruit set via autonomous self‐pollination (AS) and relate it to the magnitude of herkogamy; and (iii) evaluate if fruit abortion is a post‐pollination mechanism that determines the magnitude of pollen limitation. At each site we marked 35 plants, grouped as: unmanipulated control (C) plants subjected to open pollination, plants manually cross‐pollinated (MP), and plants excluded from pollinators and only able to self‐pollinate autonomously (AS). Fruit set was greater for MP relative to C plants providing evidence for pollen limitation, while a tendency was observed for lower fruit abortion of MP relative to C plants suggesting that fruit set is influenced not only by pollen delivery per se, but also by subsequent abortion. In addition, although pollinator visits varied significantly among populations, the magnitude of pollen limitation did not, suggesting that pollinator activity was not relevant in determining pollen limitation. Finally, fruit set tended to decrease with the degree of herkogamy for AS plants, but this result was inconclusive. These findings have contributed to identify which factors influence reproductive success in populations of R. nudiflora, with potentially relevant implications for population genetic structure and mating system evolution of this species.     

Relationship between herkogamy,incompatibility and reciprocity with pollen–ovule ratios in Melochia (Malvaceae)

Heterostyly is a floral polymorphism that increases pollination efficiency by promoting cross-pollination and reducing pollen wastage. Efficiency in pollination has been related to plant investment in gamete production and to the pollen to ovule ratio (P/O), which has been proposed as an indication of the likelihood of enough pollen grains reaching the stigmas to result in maximum reproductive success. In heterostylous species, cross-pollination is promoted by the reciprocal position of sexual organs between morphs and a heteromorphic incompatibility system, which precludes selfing and fertilizations among plants of the same morph. Morphological features like reciprocity (between morphs) and herkogamy (within morph) together with the breeding system are thought to influence pollination quality. Therefore, a close relationship between the pollination efficiency, morphological characteristics, and incompatibility would be expected. Pollination treatments and morphological measurements were carried out to describe the breeding system, herkogamy, and reciprocity of six Melochia species. Afterward, the relation between the P/O (as a surrogate of the efficiency in pollination), and reciprocity, herkogamy and incompatibility was evaluated. Monomorphic M. nodiflora and distylous M. pyramidata are self-compatible species, whereas the rest of the species are self- and morph-incompatible. There was a positive relationship between the P/O value and the degree of herkogamy and incompatibility. However, P/O values appear to increase when higher reciprocity is found in the populations. As expected, the lower values of P/O are associated with lower levels of herkogamy and compatibility in the Melochia species studied. The relationship between the factors is discussed under different scenarios of the pollinators’ predictability.     

Dioecy and the evolution of pollination systems inSchiedea and Alsinidendron (Caryophyllaceae:Alsinoideae) in the Hawaiian Islands

The transition from biotic to wind pollination and the consequencesof this transition for the evolution of dioecious breeding systems wereinvestigated in Schiedea and Alsinidendron(Caryophyllaceae: Alsinoideae), genera endemic to the Hawaiian Islands. The potential for wind pollination was studied for five species ofSchiedea using a wind tunnel. Morphological correlates of windpollination for these species were then used to infer the presence orabsence of wind pollination in the remaining Schiedea species. Hermaphroditic Alsinidendron and Schiedea species,which occur in mesic to wet forests, or less commonly in dry habitats,show little or no indication of wind pollination. These species had lowpollen:ovule ratios, large relative pollen size, diffuse inflorescences,substantial nectar production in several cases, and appear to bebiotically pollinated or autogamous. Sexually dimorphic species, whichall occur in dry habitats, are wind pollinated, based on wind tunnelresults or morphological adaptations indicating the potential for windpollination. These adaptations include high pollen:ovule ratios, smallpollen size, moderately to highly condensed inflorescences, and reducednectaries and nectar production. Shifts to wind pollination anddimorphism are strongly correlated in Schiedea, suggesting theclose functional relationship of the twophenomena.     

Enantiostyly in Chamaecrista ramosa (Fabaceae‐Caesalpinioideae): floral morphology,pollen transfer dynamics and breeding system

Enantiostyly is a form of reciprocal herkogamy, in which floral morphs present reciprocal differences in the position of sexual elements, and occurs in monomorphic and dimorphic forms. This polymorphism maximises cross‐pollination and reduces self‐pollination, being very common within the subtribe Cassiinae (Fabaceae). Nevertheless, few studies have investigated the functionality of enantiostyly, particularly in this plant group. The present study aimed to investigate enantiostyly and its functionality in Chamaecrista ramosa, a monomorphic enantiostylous shrub, in an area of coastal vegetation in northeast Brazil. Pollen deposition and capture on the body of floral visitors, the relationship of these data with floral biology and breeding system, and morph ratio were evaluated. Pollen deposition and capture occurred in specific sites of the floral visitor body, showing the functionality of enantiostyly. The floral architecture, associated with the floral visitor behaviour, resulted in indirect pollen deposition on the floral visitor body. This occurred through a loop made by the pollen upon the inner petal surface, similar that generally reported for other Cassiinae. Chamaecrista ramosa is self‐compatible, although no fruit set was observed through spontaneous self‐pollination. The occurrence and number of floral morphs was similar within clumps. Enantiostyly seems to be advantageous for this species, as it results in efficient pollen capture and deposition, reduces the chances of autogamy and maximises intermorph pollen flow.     

Floral sex ratios, disease and seed set in dioecious Silene dioica

1 In the dioecious, perennial herb Silene dioica , the density of pollen donors in a population is determined by overall plant density, the sex ratio and the proportion of plants infected with the anther-smut fungus Microbotryum violaceum , which results in permanent sterility of both male and female plants.
2 Pollinators ( Bombus spp.) were found to prefer male flowers and to avoid diseased flowers. This may result in an overall lower visitation frequency and increased risk for pollen limitation in populations with a low density of males or a high incidence of disease.
3 Compared with open-pollinated flowers, hand pollination resulted in a significant increase in the number of seeds produced per fruit in populations with an experimentally reduced proportion of males (25% and 50% male flowers) but not in a naturally male-dominated population (75% male flowers). Seed production per plant was increased by hand pollination only in the most female-dominated population. Because the floral sex ratio is often male-biased, resources rather than pollen availability are likely to set the upper limit for total seed production per individual in most healthy populations of S. dioica.
4 There was a negative relationship between seed set and incidence of disease across 22 populations in both years of a field study. However, there was no consistent difference between the responses of highly diseased populations (incidence 30–56%) and populations with a low disease incidence (incidence 0–8%) to hand pollination.
5 In a greenhouse experiment with cloned hand-pollinated females, the presence of spores on healthy flowers was found to reduce seed set significantly. In highly diseased populations, therefore, the frequent deposition of spores by flower visitors onto remaining healthy plants may decrease seed production below the potential level determined by resources or pollen availability.     

Floral morph composition and pollen limitation in the seed set of <Emphasis Type="Italic">Nymphoides indica</Emphasis> populations

We investigated the floral morph composition and seed set of the populations in a heterostylous aquatic plant, Nymphoides indica O. Kuntze (Menyanthaceae). The bias of floral morph ratio in the populations was negatively correlated with the seed set. In the populations with biased floral morph ratio, the pollen on the stigma of the common morphs were dominated by pollen of the same morph, resulting in reduced seed set. The addition of pollen of the opposite morph on the stigmas of the common morph resulted in an increase of fruit and seed set rates. The intermorph pollination rate and the fruit and seed set rates of Nymphoides indica were highest when two floral morphs were close in the populations. Various insect species including Lepidoptera, Diptera and Hymenoptera visited the flowers. However, geitonogamous pollination was common because of the short flying distance of the pollinators. These results indicate that the seed set of Nymphoides indica is limited by the shortage of compatible pollens and that the success of intermorph pollination is influenced by spatial distribution of the two floral morphs. As Nymphoides indica is endangered, conservation of the populations with high fecundity is proposed by us.     

Is Echeveria gibbiflora (Crassulaceae) fecundity limited by pollen availability? An experimental study

1. An experimental approach, manually pollinating all the flowers of individual plants, was used to measure the effect of pollen limitation on female fecundity of the hummingbird-pollinated perennial shrub Echeveria gibbiflora in the ecological preserve of Pedregal de San Angel around México City, México. Eleven randomly selected plants were manually over-pollinated in all their flowers and another 11 were left to be freely visited by natural pollinators.
2. Manually pollinated plants produced significantly more fruit and seeds than control plants (1·38 and 1·74 times, respectively). There was no change in average mass of fruits.
3. Considering individual fruit production per plant sampled three times in one season, decreases in fruit mass and average seeds per fruit were observed within the same reproductive season for both treatments. For the manually pollinated plants, from the start to the end of the reproductive season, seed set decreased 55·9%; while in control plants seed set decreased 33·4% in the same period. For both treatments, average fruit mass decreased 26%.
4. Vegetative growth was not significantly different between control and experimental plants but hand-pollinated plants showed a smaller reproduction probability for the following year.
5. It is concluded that female fecundity in E. gibbiflora is limited by pollen early in the reproductive season and by resources in the middle and the end of the season.     

两性花的雄蕊运动:多样性和适应意义

雄蕊运动指雄蕊在自身能量支持下发生的主动运动,不包括雄蕊在访花者触碰下造成的被动位移。该文总结了雄蕊的应激运动、快速猛烈弹射、缓慢运动以及级联运动等4种主要类型,分析了这些运动类型的系统分布及繁殖适应意义等方面的研究进展。雄蕊的应激运动由访花者或其他外力诱发,可能起到促进散粉和实现繁殖保障的作用;雄蕊快速猛烈的弹射运动可将花粉猛然撒向空中或访花者身上,促进了花粉的风媒或虫媒散布;缓慢运动的雄蕊可能通过在不同花期改变雄蕊的空间位置和雌雄异位程度来调节繁殖策略,或主动将雄蕊花药移至特定部位(如柱头表面)实现自交;雄蕊逐一、依次发生的级联运动较为复杂,主要分布在刺莲花科、梅花草科、旱金莲科和芸香科中,目前还缺乏实验研究;但根据\"花粉呈现理论\"以及其他类型的雄蕊运动研究结果,雄蕊的级联运动可以将花粉分批呈现给不同的传粉者,通过不同传粉者的分别传粉来提高花粉的输出;而且可避免已散粉雄蕊对即将散粉雄蕊的干扰,同时可能也降低了雌雄功能干扰和(或)花内自交。在芸香(Ruta graveolens)中,级联运动之后的雄蕊还会在花末期再同时向花中央运动;这种多向、多次运动方式是目前发现的最复杂的雄蕊运动类型。雄蕊运动领域值得今后开展进一步实验研究的方向主要有:1)雄蕊运动尤其是级联运动对雌雄功能干扰(性别间干扰)、雄蕊与雄蕊的\"性别内干扰\"等植物繁殖格局的影响;2)雄蕊运动与雌雄异熟、雌雄异位等花部特征的相互作用;3)雄蕊运动复杂类型的生理与发育机制。     

珍稀濒危沉水植物水菜花传粉生物学研究

水菜花(Ottelia cordata)是珍稀濒危的沉水植物,现仅分布在中国海南岛北部海口至文昌一带的淡水湿地,其造型优美,极具园艺观赏价值.然而,受人类活动影响,水菜花的生境急剧退缩且更加破碎化,濒临灭绝.为探究水菜花的繁殖特征和繁殖规律,该研究分析了水菜花的花部形态、性比、花粉活性、柱头可授性、反射光谱、花粉限制与无融合生殖及其传粉者类型与行为.结果表明:(1)水菜花雌雄异株,雌、雄个体的性比约为1∶2;水菜花雌、雄花形态相似,但雌花略大于雄花.(2)水菜花花粉活性和柱头可授性在花蕾期和开放期均较高.(3)中华蜜蜂(Apis cerana)是水菜花的主要传粉者,传粉效率较高且访问雄花的频率显著高于雌花.(4)水菜花雄蕊、雌蕊间的花色距离显著高于中华蜜蜂辨别的阈值(P＜0.001).(5)在自然授粉和人工授粉下,水菜花坐果率分别为95.29％和98.42％,并且不存在无融合生殖现象.综上所述,水菜花两性模拟的欺骗性传粉并不完美,传粉者可以从视觉上区分雌花和雄花;而由于水菜花雄花数量较多,传粉者低频率的\"错访\"足以达到水菜花雌花的繁殖需求.因此,在今后开展水菜花迁地保护、人工种群恢复等保育工作时,应重视水菜花种群大小、性别比例和当地传粉者种群数量.